The mode of wave propagation therein is the TE.sub.11 mode having field lines which are orthogonal to the walls which therefore do not need to be perfectly circular.
A circular wave guide for use with the TE.sub.11 mode and which is over-dimensioned for this mode has two essential advantages over a rectangular wave guide for use with the TE.sub.01 mode: its attenuation is less by a factor of about 2 or 3, thereby enabling the use of microwave transmission systems requiring less power or smaller aerials of lower gain for identical range; further the propagation of two perpendicular waves which are independent from each other instead of a single wave is equivalent to doubling the capacity of a connection or of halving the number of connections required.
Now, the present state of the art only makes it possible to manufacture circular wave guide components which are rigid, machined, and whose connecting flanges are fixed by welding or by brazing in a workshop. These rigid components are generally a few meters long, up to a maximum of six meters.
This rigidity and multiplicity of connecting flanges causes these types of realization to have several drawbacks from the electrical point of view (reflections from the flanges), from the mechanical point of view (no flexibility; transport, handling and installation difficulties) and from the point of view of economy (high manufacturing costs).
Preferred wave guides in accordance with the present invention overcome the above drawbacks.
The present invention provides a circular wave guide including a metal conductor tube, which is sufficiently flexible to be wound on a drum, and which is provided with mechanical reinforcing means against ovalizing deformation of its right cross-section, said reinforcing means being retained at least until the wave guide is installed in an operative position.
The flexibility obtained makes it possible to wind the wave guide on a drum in the same manner as a cable, yet nevertheless, in operation it is capable of conveying electromagnetic propagation with less loss than rigid guides.
Examples of the present invention are described below with reference to the accompanying drawings.